1. Field of the Invention
The present invention relates to a process for the purification of a styrenic polymer. More particularly, it pertains to a process for efficiently purifying a styrenic polymer having a high degree of syndiotactic configuration in its stereochemical structure of polymer chain to a high level of purity.
2. Description of the Related Arts
Heretofore, styrenic polymers produced by the radical polymerization or the like have had an atactic configuration in stereostructure, have been molded to a variety of shapes by various molding methods such as injection molding, extrusion molding, blow molding, vacuum molding and cast molding and have been used for electrical appliances, office machines, household goods, packaging containers, toys, furnitures, synthetic papers and other industrial materials.
Because of their atactic configuration in stereochemical structure, however, such styrenic polymers have suffered the disadvantage of inferior heat and chemical resistances.
The group of the present inventors has previously succeeded in developing styrenic polymers each having a high degree of syndiotacticity and further, has proved that styrenic polymers having syndiotactic configuration are obtained by the use of a catalyst comprising a titanium compound and a contact product (alkylaluminoxane) of an organoaluminum compound with a condensing agent (refer to Japanese Patent Application Laid-Open No. 187708/1987).
The above-mentioned styrenic polymers are produced by means of slurry polymerization, bulk polymerization or the like and preferably in a high concentration of styrene from the viewpoint of the catalyst activity and polymer productivity. In addition, it has been desired to remove the residual catalyst components in the obtained polymer by means of deashing (removal of residual catalyst).
However, the problem still unsolved in deashing was that although the polymer product polymerized at a low conversion efficiency or a low concentration of styrene was easy to deash, the polymer with a high conversion efficiency, for example 60% or higher becomes difficult to deash and clean with increase in the conversion efficiency.
As a means for facilitating the deashing, there is available a method in which a deashing agent (exemplified by a strong acid and strong base) is employed at the glass transition temperature (Tg) or lower of the polymer (Japanese Patent Application Laid-Open No. 59012/1991) or at the Tg or higher thereof (Japanese Patent Application Laid-Open No. 25133/1991). Specifically the above-mentioned method comprises the steps of sufficiently swelling the polymer by the use of a swelling agent in the presence of a deashing agent, adding a deactivating agent simultaneously with a swelling agent to the polymer to decompose the catalytic components; and then thoroughly cleaning the polymer with a cleaning solvent or the like.
However, the use of an acid as the deashing agent causes the problems such as coloration of polymer and corrosion of a molding machine at the time of molding, while the use of a base brings about the problems such as corrosion of a molding machine at the time of molding and decomposition of other resins at the time of molding. As a means for solving the aforesaid problem, mention may be made of a method in which the polymer is cleaned with a large amount of a solvent. The method, however, leads to intricate, troublesome process and unreasonably large equipment for deashing and cleaning, thus causing expensive installation cost.
Under such circumstances, intensive research and investigation were made by the present inventors in order to overcome the above-mentioned problem involved in the prior art and to develop a process wherein a styrenic polymer with a high conversion efficiency can be efficiently purified to a high level of purity.
As the result, it has been found that the aforestated problem can be solved by treating the styrenic polymer to be purified with a swelling agent and a deactivating agent. The present invention has been accomplished on the basis of the foregoing finding and information.